This invention relates to apparatus for extracting a tube from a tubesheet of a heat exchanger and slitting the tube into two parts as it is being extracted.
Condensers and other indirect heat exchangers have a large number of tubes in interference or press fit into or expanded into engagement with openings in spaced apart tubesheets to form a fluid tight seal therebetween. A fluid medium flows through the tubes while another fluid flows about or around the tubes between the tubesheets. Generally a heat transfer fluid such as water circulates through the tubes while a high temperature fluid such as combustion gases or heated water flows about the tubes and heat is transferred to the fluid within the tubes. Occasionally, it becomes necessary to remove the tubes from the tubesheet and retube the heat exchanger. Such removal and retubing may be performed when excessive scale build-up within the tubes occur, when leaks occur, as part of a preventative maintenance program, or when an excessive number of tubes become worn,penetrated or damaged in any way.
In fossil fuel power plants, when the tubes are to be extracted, the tight fit between the tubes and the tubesheets are relieved and the tubes are pulled a small distance through the tubesheet by a tube puller. Thereafter a tube traveler or extractor such as that disclosed in Harris U.S. Pat. Nos. 4,044,444 and 4,815,201 are used to completely extract each tube from the heat exchanger through the tubesheet. Such tube travelers have a pair of serrated drivers mounted on parallel shafts spaced slightly apart, the drivers being rotated in opposite directions to pull the tubes through the nip between the drivers so that the tubes are pulled and deformed from a circular to a flattened oval shape. The tubes, which may be as long as 50 to 60 feet in length, are thereafter removed to a tube chopper where they are chopped into short sections of scrap metal for recycling.
In nuclear fuel power plants, such as boiling water reactor (BWR) nuclear plants, safety regulations require that both the interior and the exterior surfaces of the tubes removed from a heat exchanger be free of contamination before they are scrapped and recycled. In the prior art either the tubes were slowly pulled from the tubesheet without deforming the tube and thereafter cut into short lengths for subsequent inspection off-site after shipping in a shielded container, or the tubes were pulled by a tube traveler and thereafter the flattened tubes were inserted into a large bulky splitter located a distance greater than a tube length from the tubesheet. The tubes had to be hand carried away from the traveler to the splitter where the flattened tubes were separated in half through the major cross-sectional dimension so that the exterior and the interior surfaces could be inspected after being chopped into scrap sections for off-site disposal or decontamination. An example of this latter process is disclosed in Hahn et al U.S. Pat. Nos. 5,276,965 and 5,293,682 where the tubes from the traveler are further flattened by a pair of serrated rollers so as to work harden the edges between the top and bottom surfaces of the flattened tube and fed to a stationary elongated wedge shaped blade which fractures and splits the deformed tube along the work hardened edges into two sections. However, as aforesaid, this apparatus provides a large bulky machine which must be located a distance of more than a tube length away from the tubesheet, i.e., 50 to 60 feet or more from the tubesheet. Thus, the entire length of potentially contaminated tube is exposed for that distance so that the area that must be protected from contamination is greatly extended. Additionally, since the tube must be carried by hand from the traveler to the splitter the process is relatively slow and makes an inefficient use of the speed of the traveler.